Melt butter in large sauce pan. Cook onions in butter until softened and translucent. Add in all spices, adjusting for flavor. Stir in coconut milk and tomato paste until well combined.
Transfer mixture to a blender or use immersion blender to puree the onions in the sauce mixture.
Add cooked meatballs to sauce and allow to cool. Store meatball mixture in a gallon sized ziploc bag. Store in the freezer for 3-4 months.
Cook in Crockpot from Frozen: Warm in crockpot on LOW for 3-4 hours. Serve with rice and naan bread.